1. Field of the Invention
This invention relates to cationic biopolymers obtained by demineralization, deproteinization, decalcification and deacetylation of fresh crustacean shells, to a process for their production and to their use for the production of cosmetic and pharmaceutical formulations.
2. Statement of Related Art
Chitosans are biopolymers which belong to the group of hydrocolloids. Chemically, they are partly deacetylated chitins varying in molecular weight which contain the idealized monomer unit (I). ##STR1## In contrast to most hydrocolloids, which are negatively charged at biological pH values, chitosans are cationic biopolymers under these conditions. The positively charged chitosans are capable of interacting with oppositely charged surfaces and, accordingly, are used in cosmetic hair-care and body-care formulations and pharmaceutical formulations (cf. Ullmann's Encyclopedia of Industrial Chemistry, 5th Ed., Vol. A6, Weinheim, Verlag Chemie, 1986, pp. 231-332). Reviews on this subject have been published, for example, by B. Gesslein et al. in HAPPI 27, 57 (1990), by O. Skaugrud in Drug Cosm. Ind. 148, 24 (1991) and by E. Onsoyen et al. in Seifen-Ole-Fette-Wachse 117, 633 (1991).
Chitosans are produced from chitin, preferably from the shell remains of crustaceans which are available in large quantities as inexpensive raw materials. Normally, the chitin is first deproteinized by addition of bases, demineralized by addition of mineral acids and, finally, deacetylated by addition of strong bases in a process described for the first time by Hackmann et al., the molecular weights being spread over a broad range.
A process for the production of a chitin degradation product is known from Makromol. Chem. 177, 3589 (1976). In this process, the Hackmann degradation is modified to the extent that the crab shells are first treated with hydrochloric acid at room temperature, then deacetylated with caustic soda solution over a period of 42 h at 100.degree. C., subsequently treated with more hydrochloric acid at room temperature and, finally, briefly aftertreated with sodium hydroxide solution, again at room temperature. In this process, the deacetylation takes place in the second step. By contrast, the concluding treatment with sodium hydroxide solution is merely carried out to "fine tune" the degree of deacetylation and, accordingly, takes place at room temperature. Although this leads to low-ash products with a high degree of deacetylation and good solubility in organic acids, the molecular weight is very low and the film-forming properties are unsatisfactory.
The book "Chitin, Chitosan and Related Enzymes" (Ed. John P. Zikakis), New York, Academic Press, 1984, pp. XVII to XXIV and pp. 239 to 255, also relates inter alia to degradation products of chitin which, although having a low ash content according to Table 1 on p. 248 ("Chitin D"), have an extremely low degree of deacetylation of only 17.1%. Unfortunately, products such as these are completely insoluble in organic acids.
French patent application FR-A 27 01 266 also describes degradation products which are obtained by first treating chitin with hydrochloric acid and then deacetylating it as far as possible with sodium hydroxide solution. The products obtained typically have a degree of deacetylation of 92% and are distinguished by a very low calcium carbonate content, are readily soluble in organic acids and give low-viscosity products. However, a major disadvantage once again is that the molecular weight is very low on account of the drastic degradation conditions and the film-forming properties of the products are again unsatisfactory.
Finally, WO 91/05808 (Firextra Oy) and EP-B1 0 382 150 (Hoechst) describe processes for the production of optionally microcrystalline chitosan.
To sum up, it may be said that known cationic biopolymers can be divided into two groups: the first group of products includes those which have a high degree of deacetylation, are soluble in organic acids and form low-viscosity solutions, but do not have satisfactory film-forming properties. The second group includes products which have a low degree of deacetylation, a relatively high molecular weight and good film-forming properties, but are poorly soluble in organic acids and, accordingly, are difficult to make up.
In addition, known products have a number of other disadvantages. As a result of the drastic degradation, they are generally heavily discolored, have an unacceptable odor and lack stability in storage, i.e. viscosity does not remain constant, but decreases, in the event of prolonged storage. Moreover, preservatives unfortunately have to be added because the products are susceptible to contamination by microorganisms.
Accordingly, the complex problem addressed by the present invention was to provide new cationic biopolymers which would be free from the disadvantages mentioned above, i.e. which would have a high molecular weight but would still be readily soluble in organic acids, forming low-viscosity solutions therein, and which would show excellent film-forming properties despite a high degree of deacetylation.